Mineral oil composition



Fat-ented jan. 6, 1942 ED STATES OFFER MINERAL 0E COIVIPOSITHON rationoi New York No Drawing. Application May 31,

Serial No. 276,616

9 Claims.

This invention is concerned with the stabilization of viscous mineraloil fractions against the harmful effects of oxidation or deteriorationwith use by means of an oxidation inhibitor or an antioxidant. Theinvention is more specifically related to the improvement orstabilization of such mineral oil fractions by the use of novelcompounds, or a novel class of compounds, which when admixed with aviscous mineral oil in minor proportions will prevent or delayundesirable changes taking place in the oil.

As is well known to those familiar with the art, substantially all thevarious fractions obtained from mineral oils and refined for theirvarious uses are susceptible to oxidation; The susceptibility of an oilfraction to oxidation and the manner in which oxidation manifests itselfwithin the oil varies with the type and degree of refinement to whichthe oil has been subjected and with the conditions under which it isused or tested. In other words, the products formed in an oil fractionas a result of oxidation and the degree to which they are formed.depends upon the extent to which the various unstable constituents orconstituents which may act as oxidation catalysts have been removed byrefining operations, and also upon the conditions of use.

A highly refined viscous oil, for example, which is one that has beenrefined by treatment with fuming sulfuric acid or other means orcombinations such as A1Cl3, solvents and acids (or with large quantitiesof concentrated sulfuric acid), tends to form relatively large amountsof acidic constituents when subjected to oxidizing conditions. Thepresence of a catalytic material such as copper does not appear toaffect appreciably the oxidation of highly refined oils and such oilsare less prone to the formation of colored bodies or of insolublesludge. The formation of acidic bodies, however, is highly undesirablefor most applications of these oils. For example, when used as aninsulating or cooling oil in elec-' trical equipment such astransformers or capacitors an increase in acidic bodies tends to lowerthe dielectric strength of the oil and has other harmful eifects whichare undesirable. The acids are corrosive to metals and thus reduce theuseful life of the oils as lubricants or for other purposes in whichthey come in contact with metals,

and the acidic materials are also injurious in textile lubricants and inspray oils.

Moderately refined oils, which are normally oils that have been refinedby treatment with only moderate amounts of sulfuric acid, or otherrefining agents, tend to form relatively small amounts of acidicoxidation products as compared with highly refined oils, but theyundergo material color depreciation and form considerable amounts ofsludge. The changes taking place in these oils are appreciablyaccelerated by the presence of metal catalysts such as copper.Sufiicient acid is generally formed to cause some reduction in thedielectric strength of these oils, but the principal objection to themis their tendency to deposit sludge which interferes with heat transferin transformers and turbines and also causes plugging of oil feed linesin lubricating systems.

"Solvent-refined oils in general which have been prepared by treatmentwith selective solvents, such as chlorex, phenol, furfural, etc.,resemble the moderately refined acid-treated oils in that theiroxidation is accelerated by the presence of metals such as copper andfurther in that it is attended by substantial color depreciation andsludge formation. Acid formation is usually greater than in the case ofmoderately acidrefined oils, but considerably less than with highlyrefined oils. -Both sludge and acid formation lower their value for manypurposes, such as electrical insulation, lubrication, etc. Also,solvent-refined oils have found extensive use as lubricants for internalcombustion engines because of their high viscosity index, but under theconditions of use encountered in crankc'ases such oils developconstituents which are corrosive toward certain metal bearings such asthe cadmiumsilver bearing, etc., which are sometimes used.

It is to be understood that this classification of oils as highlyrefined, moderately refined and solvent-refined is by no means limitingand that there can exist oils whose refining and blending has been suchas to make them intermediate in properties betweenthe types set up.Thus, response to inhibitors may be said to depend entirely upon thetype of oxidation and end products of oxidation of'an oil, which in turndepends largely upon the degree of refining this oil has had. Further,the degree of refining required to produce these types of oils varieswith the crude source so that any one refining procedure may produceeither a highly refined oil or a moderately refined oil, depending uponthe crude source. Pennsylvania type oils, for example, require much lessrefining to produce highly refined oils than the Coastal type of oils.

The use of oxidation inhibitors for the purpose of stabilizing a viscousmineral oil fraction against the deleterious effects of oxidationdiscussed above is well known. Since the action of the problem of theirdevelopment is a difiicult one and is evidently influenced to a largedegree by the oxidizable constituents which are in the.

oil following a particular refining treatment. Thus, a particularinhibitor or class of inhibitors may be effective to stabilize a highlyrefined oil oil against acid formation while the same inhibitor may haveno appreciable effect upon acid, color or sludge formation in amoderately refined oil and vice versa. This same inhibitor may or maynot be effective in inhibiting acid, sludge and color formation in asolvent-refined oil and may or may not be effective to inhibit thecorrosive action of a solvent-refined oil toward metals such as used incadmium-silver bearings.

This invention is particularly concerned with the inhibition ofoxidation in highly refined oils of the type used in transformers,turbines, and the like through the use of a novel class of compounds tobe hereinafter described. The compounds contemplated herein do notappear to be effective negative catalysts toward the oxidation ofmoderately refined or solvent-refined oils of the turbine oil type, butthey are effective to inhibit the corrosive action of solvent-refinedmotor oils toward alloy metals, such as cadmiumsilver alloy bearings,under conditions encountered in crankcase use.

This invention is predicated upon the discovery that a group of organiccompounds which we may broadly classify as thiazane and itsN-substituted derivatives are effective to inhibit the deleteriouseffects of oxidation upon certain types of viscous mineral oils.

More specifically, the addition agents or antioxidants contemplated bythis invention are members of the specific class of thiazanes known asthe thiomorpholines, which are characterized by the general formula ,inwhich R represents a radical selected from the group consisting ofhydrogen, alkyl, aryl, and alkaryl radicals or groups. When R. in theabove formula is hydrogen the compound is thiomorpholine, the remainingcompounds comprehended by the formula beingbroadly classified herein asN-substituted derivatives of thiomorpholine or N- substitutedthiomorpholines.

To demonstrate the effectiveness of these thiomorpholine compounds asantioxidants for viscous mineral oils, N-amyl thiomorpholine waspreparedby the procedure of Lawson and Reid, Journal American ChemicalSociety 47, 2828 (1925), using the crude material after topping off anyamylamine which might have been present.

The following examples in which the N-amyl, thiomorpholine was used as arepresentative compound within the class, illustrate the effectivenessof these compounds as anti-oxidants or oxidation inhibitors for viscousmineral oils.

hours.

aacaasa these inhibiting materials is apparently catalytic,

EXAMPLE I Highly refined oil The oil employed in this test was of thehighly refined type used in transformers and the like which had beenobtained from a Coastal distillate by successive treatment with 40 lbs.per bbl. of 98 per cent sulfuric acidand 180 lbs. per bbl. of 103 percent Oleum, followed by neutralization, washing and clay percolation. Ithad a specific gravity of 0.871, a flash point of 310 F. and a Sayboltviscosity of 69 seconds at'100 F.

The test used, known as the modified German tar test, involved heating a150 gram sample of the oil at a temperature of 120 C. while bubblingoxygen gas through the oil for a period of The quantity of acidicoxidation products thus formed in the oil was determined by titrationwith standard alkali and the results recorded in terms of neutralizationnumber (N. N.) which represents the milligrams of KOH required toneutralize the acid in one gram of oil. The results obtained with theoil alone and with the same oil inhibited with N-ampl thiomorpholine aregiven in Table I below:

EXAMPLE II Solvent refined motor oil The oil used in this test was amotor oil obtained by refining with chlorex a Pennsylvania -neutralstock and a Pennsylvania residual stock and blending to produce an oilof the following properties: specific gravity 0.872; flash point 435 F.,Saybolt viscosity 318 seconds at F.

The test involved immersing a 6 gram section of a cadmium-silver bearingin a 30 gram sample of the oil, heating the oil to a temperature of C.,and bubbling air therethrough against the surface of the bearing for aperiod of 22 hours. Two specimens from the same bearing were testedsimultaneously, one in the oil alone and the other in the oil containingthe inhibitor, the comparative weight loss of the bearing specimensindicates the extent to which corrosion has been retarded by thethiomorpholine. The results of this test are given in Table II below:

Table II ()il Weight loss JUN/[grams Oilalonc 543,0 0il+0.25}1,N-amylLhiorriurpholinc. v 2.0

It will be understood that a suitable solvent such as benzol, toluol andrelated hydrocarbons; carbon tetrachloride etc. may be employed ifdesired to facilitate solution of the improving agent in the oil; alsothat the compounds contemplated herein may be used in varying amountsdepending upon the oil fraction, conditions of use, etc., but for thepurposes contemplated herein it will be found that in general the use ofthiazanes in proportions ranging from about 0.10% to about 5.0% willgive satisfactory results.

It is to be further understood that the terms highly refined, and solvenrefined as used herein have reference to oils correspondingsubstantially in their manner of deterioration and inhibitor response tothe examples given hereinabove and are not necessarily restricted to anoil obtained by particular refining operation. As has been previouslypointed out, the final characteristics in an oil fractlolliare efiectedby the crude from which the oil is obtained as well as by the refiningtreatment. For example, an oil of the -.,highly refined type may beobtained from a selected crude by a refining treatment which withanother crude stock would yield a moderately refined" oil.

We claim:

1. An improved mineral oil composition comprising a viscous mineral oilfraction having in admixture therewith in minor proportion, sufiicientto inhibit the deleterious efiects of oxidation on said oil, a compoundhaving the general formula:

H2 H2 -0 s\-- /N-R (1-0 H: H: v in which R represents a radical selectedfrom the group consisting of alkyl, aryl and alkaryl hydrocarbon groups.

2. An improved mineral oil composition comprising a viscous mineral oilfraction selected from the group consisting of highly refined oils andsolvent refined motor oils having in admixture therewith a minorproportion, suflicient to inhibit the deleterious efiects of oxidationon said oil, a compound having the general formula:

H7 H: c-c s N--lt in which R represents a radical selected from thegroup consisting of alkyl, aryl and alkaryl hydrocarbon groups. I

3. A highly refined viscous mineral oil fraction having an N-substituted thiomorpholine in admixture therewith in minor proportionsufficient to inhibit the deleterious efiect of oxidation on said 011. V

4. A highly refined viscous mineral oil fraction rosive to alloybearings, typified by cadmiumsilver bearings, under conditions of use.encoun-,

tered in the operation of an internal combustion engine, said oil havingin admixture therewith a minor proportion, sufficient to inhibit saidcorrosive action, of a compound having the general formula V in m H2 H2in which R represents a radical selected from the group consisting ofalkyl, aryl and alkaryl hydrocarbon groups.

7. A viscous mineral oil fraction normally corrosive to alloy bearings,typified by cadmiumsilver bearings, under conditions of use encounteredin the operation of an internal combustion engine, said oil having an N-substituted thiomorpholine in-admixture therewith in minor proportionsufiicient to inhibit said corrosive action.

8. A viscous mineral oil fraction normally corrosive to alloy bearings,typified by cadmiumsilver bearings, under conditions of use encounteredin the operation of an internal combustion engine, said oil havingN-amyl thiomorpholine in admixture therewith in a minor amountsufficient to inhibit said corrosive action.

9. A viscous mineral oil fraction normally corrosive to alloy bearings,typified by cadmiumsilver bearings, under conditions of useencounteredin the operation of an internal combustion engine, said oilhaving about 0.25% N-amyl thiomorpholine in admixture therewith toinhibit said corrosive action.

ROBERT C. MORAN. DARWIN E. BADER'I'SCHER. HENRY G. BERGER.

